Map top level meta data from ITopLevelDocument rather than IObjectMetaData

src/NJsonApiCore/Serialization/JsonApiTransformer.cs

@@ -54,7 +54,7 @@ public CompoundDocument Transform(object objectGraph, Context context)
 
             var result = new CompoundDocument
             {
-                Meta = transformationHelper.GetMetadata(objectGraph)
+                Meta = transformationHelper.GetTopLevelMetadata(objectGraph)
             };
 
             var resource = transformationHelper.UnwrapResourceObject(objectGraph);

src/NJsonApiCore/Serialization/TransformationHelper.cs

@@ -164,11 +164,11 @@ public object UnwrapResourceObject(object objectGraph)
             return objectGraph;
         }
 
-        public IMetaData GetMetadata(object objectGraph)
+        public IMetaData GetTopLevelMetadata(object objectGraph)
         {
-            if (objectGraph is IObjectMetaDataContainer)
+            if (objectGraph is ITopLevelDocument)
             {
-                var metaDataContainer = objectGraph as IObjectMetaDataContainer;
+                var metaDataContainer = objectGraph as ITopLevelDocument;
                 return metaDataContainer.GetMetaData();
             }
             return null;

test/NJsonApiCore.Test/Serialization/JsonApiTransformerTest/TestMetaData.cs

@@ -48,6 +48,7 @@ public void Creates_CompoundDocument_for_single_class_with_metadata_and_properly
             var transformedObject = result.Data as SingleResource;
             Assert.Equal("value1", transformedObject.MetaData["meta1"]);
             Assert.Equal("value2", transformedObject.MetaData["meta2"]);
+            Assert.Null(result.Meta);
         }
 
         [Fact]